Correlated studies of the structure and function of ganglion cell axons in the optic nerve head and nerve fiber layer of the primate retina will be made. Function will be studied in monkeys with microelectrode recordings of single nerve fibers driven orthodromically by electrical stimulation of the retina and antidromically by stimulation of optic chiasm and parvocellular or magnocellular lateral geniculate nucleus (LGN). Structure will be studied in monkey by light and electron microscopy of single fibers labeled by horse radish peroxidase. Spaced and continuous series of serial sections will be reconstructed by computer to reveal the transretinal and intra-disc position of individual fibers. Fiber size spectra of fascicles of the accurate bundles will be prepared, of human and monkey tissue. The functional data will relate conduction velocities of the myelinated and unmyelinated segments of the same fibers to laminar position within a given fascicle and to terminal position with the LGN. The structural data will test the hypothesis that the nerve fiber layer is laminated with peripheral fibers overlying central fibers. These data relate to the pathophysiology of visual loss in glaucoma.